This invention relates to medical devices, and in particular to angiographic catheters. Angiographic catheters are long, narrow, thin-walled tubes that are percutaneously inserted into the human or animal vascular system for therapeutic or diagnostic purposes. Most diagnostic catheters have a series of side-holes in varied configurations near the distal end, as well as an open end-hole at the distal end tip. The end-hole allows the catheter to be passed over and guided by a wire which has been inserted into the vascular system through a hollow cannula placed in a blood vessel, after which the guide wire is withdrawn. The smaller side-holes and end-hole allows injection of radiopaque contrast material into the blood stream surrounding the distal end, so as to produce an image of the outline of a chamber or a blood vessel (an angiogram) on X-ray film or other graphic medium. During the diagnostic angiography process, the contrast material is normally injected at a rapid rate using a power injector. The contrast material is forcefully discharged from the end-hole and side-holes at the distal end of the catheter.
Problems with forceful discharge of contrast material through the end-hole and smaller side-holes of an angiographic catheter are manifest. Forceful discharge can create a jet effect. The end-hole jet effect produces undesirable recoil of the catheter, thereby shifting the catheter from a desired position within a chamber or a vessel, e.g. aortic root. Catheter jets can also produce a dangerous complication, subintimal injection of the contrast material, in which the jets tunnel into the wall of the blood vessel, sometimes resulting in acute occlusion of the vessel and in a chamber like left ventricle can cause subintimal injection resulting in significant damage to endothelium. When dye is injected in a chamber like left ventricle, an end-hole or side-hole jet can also cause premature ventricular contractions (PVCs), ventricular tachycardias (groups of three or more PVCs) and other arrhythmias which endanger the patient, lengthen the time of exposure to X-rays required for satisfactory opacification, and often result in unintelligible chamber opacification in an angiogram made during their occurrence.
A further complication resulting from pressurized discharge of contrast material through the end and side-holes of known catheters is the need for more contrast material than is optimally desired to produce the angiogram. Available angiographic catheters require as much as 50 to 55 milliliters (ml) of contrast material to satisfactorily outline a human ventricle. Currently available contrast material can cause undesirable generalized allergic reactions like anaphylaxis and renal failure. Also, the amount of material used dictates the time required to inject the material and, therefore, affects both the required length of exposure to dangerous X-rays as well as the probability of obtaining a satisfactory angiogram. There is, therefore, a need in the field to reduce the amount of contrast material used in cardiac angiography.
Most catheters presently used for rapid flush angiography are configured with a circular loop or "pigtail" at the distal end. These pigtail-type catheters are provided with a plurality of side-holes through which only approximately 40% of the contrast medium is discharged at the desired position within the chamber. Although the looped end of the catheter decreases somewhat the chance of subintimal injection, the open end-hole still allows approximately 40% of the contrast material to exit the end-hole. The material exiting the end-hole creates a strong jet of material placed away from the optimal position for vessel or chamber opacification. To overcome the limitations of the pigtail catheter in cardiac angiography, various modifications have been attempted to the pigtail configuration, such as a bend at an acute angle in the distal portion of the catheter and adding multiple holes on the shaft, both to decrease the jet effect. However, these modifications have not satisfactorily alleviated the problems associated with the use of any catheter which has an open end-hole.
The smaller side-holes located adjacent the distal end of known angiographic catheters are flawed as well. Such side-holes allow a very limited volume of material to form the bolus needed for opacification of the chamber, thereby elongating the time needed to adequately outline the chamber in the angiogram. Longer X-ray exposure endangers the patient and decreases the likelihood of obtaining satisfactory angiogram results. Moreover, side-holes can cause pressure jets leading to PVCs and other arrhythmias, as outlined above.
Although adding additional side-holes may increase the volume of material allowed into the vessel while dissipating pressure jets, such an increase may result in a distal region of less strength than the main body of the catheter tube. As a result of this reduced strength, complaints have arisen as to some currently-available angiographic catheters from physicians, who have reported that in clinical use, as they have attempted to put the pigtail tip through the aortic valve, the distal tip area in which the side-holes reside sometimes buckles.
It is therefore desirable to increase the volume of the bolus of contrast material allowed to flow out of an angiographic catheter in a short time span without decreasing the catheter's rigidity near the distal end, and without inducing PVCs, ventricular tachycardias or other arrhythmias. It is also desirable to decrease the amount of material needed to create the bolus of material within the opacified vessel.